This paper analyzes the political economy of establishing bilateral trade in green certificate markets as one step towards harmonization of European green electricity support systems. We outline some of the economic principles of an integrated bilateral green certificates market, and then discuss a number of issues that are deemed to be critical for the effectiveness, stability and legitimacy of such a market. By drawing on some of the lessons of the fairly recent intentions to integrate a future green certificate market in Norway with the existing Swedish one, we highlight, exemplify and discuss some critical policy implementation and design issues. These include, for instance, the system's connection to climate policy targets, the role of other support schemes and the definition of what green electricity technologies should be included. Furthermore, the establishment of an international market presumes that the benefits of renewable power (e.g., its impacts on the environment, diversification of the power mix, self-sufficiency, etc.) are approached and valued from an international perspective rather than from a national one, thus implying lesser emphasis on, for instance, employment and regional development impacts. A bilateral green certificate system thus faces a number of important policy challenges, but at the same time it could provide important institutional learning effects that can be useful for future attempts aiming at achieving greater policy integration in the European renewable energy sector.